Jesus

OK, my brother got this new PC so I installed arma 2 through my account to show him the game. After he liked it we bought one for him too. But now all the time We try to play a multiplayer game together we can't. If he enters first and I try to connect I get kicked, and if I enter first he gets kicked. I realised That on Dayz he is using the same equipment as I am and I've read that you can keep your equip by using the same cd key. Therefore I'm thinking even though we are using different steam accounts with different cd keys the game somehow is still logging with his computer using the same cd key of my account back when I was showing him the game. I clicked on the steam library, each account has a different cd key. I Don't think this is a mod/addon related thing, but if it is I would gladly move it to the correct forum space.

And how do I delete the key? simply click on the icon and press delete? Or should I alter the file(assuming this is a file). Sorry if this look obvious, but I'm not used to using this regit tool, and I really dont wanna mess up any file or whatever this tool interfere. Thnx anyway

I must add that it's like the game does not change the cd key, and keep the cd key from when I installed It(with my account, not my brothers wich is currently in use). Is there anyway to force the game to recognize the correct cd key(my brother's, instead of mine)? Or to remove the cd-key information that belonged to my account? I mean, assuming it is a cd key problem wich i have no technical expertise to confirm.